This brief, humor-filled novel follows an engaging girl during the course of a school year on a small island off the coast of Maine. Pru Stanley is having a terrific year: she makes a new friend on the mainland after responding to a message in a bottle, her parents surprise her with a pony on her ninth birthday and she grows close to Nicholas, a fellow student at her one-room school who has moved to the island from New York City. But she is convinced that Miss Sparling, ""the best teacher in Maine,"" will follow the example of her predecessors and leave the island after a year, due to loneliness (""It didn't seem lonely to Pru. Forty-nine people lived on the island. That was plenty of friends""). And Nicholas and his parents are due to depart Seal Island when summer arrives. From Mr. Farnum at the general store and Captain Hill at the helm of the ferry boat (a key figure in two of the novel's surprises) to the lobstermen and seals, the author peoples the volume with colorful characters and palpably describes the rhythms of island life. The book starts out strong, then at times seems sketchy, jumping from one season to the next. But by story's end, all of Pru's problems are solved--with some unexpected bonuses, and snappy, credible dialogue keeps this illustrated novel moving at a brisk clip. Final artwork not seen by PW. Ages 7-10. (Mar.)